Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes where self injection of administration enables to conduct effective management of their disease.
In certain types of prior art medication delivery devices, such as fluid delivery pen type devices, cartridges of medication are used. The medication fluid to be used in the fluid delivery pen may be related to insulin regimen and varies from patient to patient and depends on the type of insulin to be injected (slow, medium, fast acting, or specific combinations of these), the lifestyle of the patient, the circumstances, patient's actual medical condition etc.
The prior art fluid delivery pen devices disclose piston rod or plunger rod whose engagement with a stopper or bunger of the cartridge facilitates the discharge of the medicament on its forward movement due to movement of the piston rod or the plunger rod on application of the force. The prior art fluid delivery pen devices with hollow piston rod having an internal thread have many advantages and is described in the U.S. Pat. No. 7,771,398 and referenced here with. A piston rod that has an internal non-locking helical thread can be substantially larger in diameter and will have a structurally efficient hollow cross section making it substantially stronger than an equivalent externally threaded rod. Further an injection device that has a direct mechanical drive between the person applying the injection force and the hollow piston rod being driven forward to inject the medicament. This ensures the person is aware of any problems in the dose delivery. The dose setting means as disclosed in (US '398) uses a bi-directional ratchet that produces tactile and auditory clicks when the outer dose-knob is rotated in order to set a dose. The audibility of dose setting means auditory clicks in (US '398) are uniform and same both when the dose is set and when the set dose is reduced.
Further the prior art hollow piston rod disposable fluid delivery pen are bigger in size. Further inner housing distal edge and the fluid cartridge holder or cartridge cover proximal edge are joined chemically or ultrasonically. Prior art hollow piston rod pen device may have external pen cap or pen lid orientation which may not be not only aesthetically presentable but also weak snap on feature to the fluid cartridge holder resulting in improper protection to the inner components. There may not be any audible click as the dose dial returns to “0”. Shorter length and shape of the thumb pad/dose button may lead to incorrect dose of delivery.
In the case of patients who are old, infirm or physically impaired or having hearing impairment the only other way of recognizing or identifying the dose set is by visual indication through the magnifying lens the numerals displayed on the dose setting member. The prior art ascertainment of dose set by visual indication through magnifying lens falls short of expectation when such patients are also visually impaired. Hence there is a need to develop a mechanism by which when a dose set or a set dose is changed or reduced is recognizable by variation in the degree of sound of the clicking i.e. preferably of higher audibility when the dose is set and of relatively lower audibility when the dose is reduced. More so in the case of diabetic patients when the drug is insulin or insulin analogue which will have to be self administered too frequently in small doses accurately.
Further the prior art pen devices dose setting clicks are by means of unidirectional ratchets or occasionally bi-directional ones which produce uniform sound while the dose is being set or reduced or the dose is being delivered as in US 20110034878. The closest prior art dose setting mechanisms are enumerated below.
In EP 608 343 is described a fluid delivery pen having a dose setting mechanism wherein the dose is set by rotating a button relative to a housing to set a dose. The button is through a ratchet coupled to a driver, the ratchet forming a unidirectional coupling which during the rotation of the button in one direction to set a dose rides or clicks over the teeth of the ratchet. In U.S. Pat. No. 6,004,297 disclosure a pawl mechanism working between the driver tube and housing is used to produce click mechanism. In US 20090254047 a connector pipe 80, ratchet 100, protrusion 83 and track 101 combination perform the click sound. In US 20090299297 the shield 10 is axially slidable in the housing 30 but rotational locked to the housing 30 by the protrusion 11 sliding in the track 31. A rim of shield teeth 12 on the proximal end of the shield 10 interact with a corresponding rim of push button teeth 2 provided on the inside of the push button 1. In US 20080287883 a shield 60 is axially slidable mounted to the housing 10. The shield 60 is provided with a protrusion 61 sliding in a longitudinal track 12 provided on the inside surface of the housing 10. In US 20110034878 while the piston rod 307 moves axially to expel the set dose the tip 327 of the click finger 326 rides over the teeth 395 of the piston rod 307 being distributed between two consecutive larger teeth 396, thereby providing an audible feedback mechanism indicating to the user through audible clicks that the dosage is progressing.
The frictional reduction in all the prior art injection pen devices occurs when a user pushes on the push button (or injection button or dose button or thumb pad as they are known by various names), the force applied may be directed to the forward movement of the driving part and the frictional reduction may be brought about by forming a pivot bearing between the two parts. One of the means of reducing friction between the two components may be by minimizing the surface area of interaction between the two objects by virtue of which the radius of resulting friction force can be kept at a minimum.
Firstly these prior art fluid delivery pen devices disclose piston rod or plunger rod with an external thread whose engagement with a stopper or bunger of the cartridge facilitates the discharge of the medicament on its forward movement due to movement of the piston rod or the plunger rod on application of the force. Secondly, the thumb pad connection for an injection pen device which minimizes the forces a user most apply to inject a dose requires relative rotation to each other between the thumb pad and the mating component i.e. the driving part with which the thumb pad mates. The thumb pad connection to a fluid delivery pen device in some of the closest prior arts with a piston rod of external thread mechanism is enumerated below.
EP 1003581 discloses an injection device in which according to FIG. 15-16 comprises a scale drum, a bushing and a push button. The scale drum and bushing rotate together and the push button and bushing rotate relatively to each other. WO 2005/018721 discloses an injection device in which the push button is formed with a bore encompassing a stem on a sleeve member. The push button and the stem are welded together such that the push button and the sleeve member are axially and rotatably fixed to each other. US 20100145282 disclose an injection device in which at least one radial bearing between the push button and the protrusion is formed in the upper and lower area.
Unlike prior art fluid delivery pen devices with external threaded rods, minimization of the forces a user must apply to inject a dose achieved by frictional reduction when a user pushes on the thumb pad in prior art fluid delivery pen devices having hollow piston rod with an internal helical thread is still an unmet need more so as envisaged in the present invention having firstly an end of dose mechanism and secondly variable audibility features incorporated while dose setting or reduction of higher set dose.
Hence it is an objective of the present invention to address the various inadequacies in accurate dose setting and ease of dose delivery by patients having poor vision/hearing in the prior art fluid delivery disposable pen devices comprising a hollow piston rod with internal helical thread.
It is another objective of the present invention to have an end of dose mechanism in a fluid delivery disposable pen device comprising a hollow piston rod with internal helical thread.
Also it is an objective of the present invention to address this necessity of unmet need for frictional reduction which minimizes the forces a user must apply to inject a dose in a fluid delivery disposable pen device with a hollow piston rod with an internal thread having an end of fluid dose mechanism and variable audibility features while dose setting or reducing the dose set.
It may also be noted that in prior art fluid delivery pen devices that after repeated self administration of fluid, fluid runs low in the cartridge, and a user may attempt to set a dose that exceeds the amount of medication left in the cartridge. Further in certain other fluid delivery pen devices towards a better accuracy, a drug delivery device may be designed not to allow a user to dial a dose that is greater than the amount of medication remaining in the cartridge. In such fluid delivery pen devices there could be wastage of the fluid. Hence it may be necessary to avoid wastage of fluid in disposable fluid delivery pen device and the need to develop a mechanism wherein not only the entire fluid in the cartridge may be delivered (the remaining amount of the fluid in the cartridge to the practically allowable barest minimum) but also the dose setting mechanism may indicate the amount of fluid yet to be delivered when the last dose set is delivered. This may enable the user to set this dose and get it injected from a new fluid delivery disposable pen device. For example, when the last dose set in a disposable delivery device may be say 60 IU (International Units) of insulin, the amount of insulin remaining in the cartridge may be 50 IU, then an end of dose mechanism of the present invention may display 10 IU in the dose setting window after delivering 50 IU of insulin and by which the patient would still know that the balance 10 IU may have to be delivered.
The drug delivery pen device last dose lock-out mechanism or an end of the dose content mechanism have been reported in the prior arts in US20090275916, US20080243087, US2010324494, US2009137964, US20080108953 and US0090240195, the disclosures of which are incorporated herein by reference. These prior art devices necessarily have piston rod or plunger rod which have threads provided on their external surfaces.
US20090275916 discloses a dosing mechanism for a medication delivery device comprising a dose setting limiting mechanism with a dose limiting member. US20080243087 discloses an end of content mechanism which may be positioned in the space defined by the inner walls of a driver wherein an outer surface of driver may be directly coupled to the inner surface of a drum scale of an injection device. US20100324494 discloses a dose setting mechanism which comprises a rotatable shaft having a first pitch in the first portion and a second pitch in the second portion of the rotatable shaft. US 20090137964 discloses an injection device comprising a track coupled to one of the housing or the dose setting member. US20080108953 discloses an injection device comprising different threaded rods and internal thread including several contact faces. US20090240195 discloses a lock for an injection device including a threaded rod, wherein the lock includes one of an anti-rotation or claw-type securing element.
It may be observed that all of the above prior art fluid delivery pen devices having an end-of-content mechanism comprises an external threaded plunger or piston rod which engages with the stopper or bunger of the cartridge for dispensing the medicament. It may further be observed that the above prior art devices makes use of either an existing rotatable or a moving member or a separate component for achieving the last dose lock out mechanism. For example in US20090275916, a dose limiting member, in US20080243087, a limiter coupled to the driver, in US US20100324494, a last dose lock-out mechanism comprises a rotatable shaft and a non-rotating member, In US 20090137964, a nut member, In US US20080108953 and US20090240195, a rotating sleeve.